[MAJOR] complete support and doc for tcp-splicing

The tcp-splicing code has been merged, and a doc has been written.
A configuration example has been derived from the previous content
switching sample.
diff --git a/src/backend.c b/src/backend.c
index f7dd675..c0283d2 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -41,6 +41,10 @@
 #include <import/ip_tproxy.h>
 #endif
 
+#ifdef CONFIG_HAP_TCPSPLICE
+#include <libtcpsplice.h>
+#endif
+
 /*
  * This function recounts the number of usable active and backup servers for
  * proxy <p>. These numbers are returned into the p->srv_act and p->srv_bck.
@@ -364,6 +368,13 @@
 		return SN_ERR_PRXCOND; /* it is a configuration limit */
 	}
 
+#ifdef CONFIG_HAP_TCPSPLICE
+	if ((s->fe->options & s->be->beprm->options) & PR_O_TCPSPLICE) {
+		/* TCP splicing supported by both FE and BE */
+		tcp_splice_initfd(s->cli_fd, fd);
+	}
+#endif
+
 	if ((fcntl(fd, F_SETFL, O_NONBLOCK)==-1) ||
 	    (setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, (char *) &one, sizeof(one)) == -1)) {
 		qfprintf(stderr,"Cannot set client socket to non blocking mode.\n");